| PNET | peripheral neuroepithelioma; primitive neuroectodermal tumor |
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| PTA | Primitive trigeminal artery |
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| PHSC | primitive hematopoietic stem cell |
| PS | primitive streak |
| primitive pit | The depression in the primitive node that serves to connect the notochordal canal with the surface ectoderm and the yolk sac. These connections are referred to as the neurenteric canal. (05 Mar 2000) |
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| primitive reticular cell | A cell with processes making contact with those of other similar cell's to form a cellular network; along with the network of reticular fibres, the reticular cell's form the stroma of bone marrow and lymphatic tissues. (05 Mar 2000) |
| primitive ridge | One of the paired ridge's on either side of the primitive groove. (05 Mar 2000) |
| primitive streak | An ectodermal ridge in the midline at the caudal end of the embryonic disk from which arises the intraembryonic mesoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and gives a cephalocaudal axis to the developing embryo. Synonym: germinal streak. (05 Mar 2000) |
| neuroectodermal tumour, primitive | A malignant brain tumour sharing common features and biologic properties with medulloblastoma. Some pathologists and clinicians use the terms interchangeably: they both can disseminate throughout the nervous system and, in some cases, systemically. most lesions arise from the posterior fossa in children under five years of age. The tumour often produces hydrocephalus and symptoms of increased intracranial pressure. Papilledema is often present. (12 Dec 1998) |
| amniotic fold | A fold of amniotic membrane enclosing the yolk stalk and extending from the point of insertion of the umbilical cord to the yolk sac; in reptiles and birds it is the reflected edge of the amnion where it folds over to cover the embryo during early development. Synonym: Schultze's fold. (05 Mar 2000) |
| anterior axillary fold | Bounds axilla anteriorly; formed by skin and fascia overlying inferior border of pectoralis major muscle. (05 Mar 2000) |
| aryepiglottic fold | A prominent fold of mucous membrane stretching between the lateral margin of the epiglottis and the arytenoid cartilage on either side; it encloses the aryepiglottic muscle. Synonym: plica aryepiglottica. (05 Mar 2000) |
| axillary fold | One of the folds of skin and muscular tissue bounding the axilla anteriorly and posteriorly. Synonym: plica axillaris. (05 Mar 2000) |
| palpebronasal fold | A fold of skin that comes down across the inner angle of the eye. The epicanthal fold is more common in children with Down syndrome and other birth defects than normal children and so is of value in diagnosis. Although some dictionaries state that this eye fold is found in peoples of Asian origin, this is not true. The normal Asian eyefold is continuous with the lower edge of the upper eyelid and actually appears distinctly different than a true epicanthal fold. (12 Dec 1998) |
| vascular fold of the caecum | <anatomy> A peritoneal fold that arches over a branch of the ileocolic artery and bounds in front a narrow recess, the superior ileocaecal (or ileocolic) recess. Synonym: plica caecalis vascularis. (05 Mar 2000) |
| malar fold | An ill-defined groove in the skin that extends downward and medially from the lateral canthus. (05 Mar 2000) |
| Vater's fold | A fold of mucous membrane in the duodenum just above the greater duodenal papilla. (05 Mar 2000) |
| mallear fold | One of two ligamentous bands, anterior and posterior, making folds on the tympanic side of the tympanic membrane extending from each extremity of the tympanic notch to the malleolar prominence; they mark the boundary between the tense and the flaccid portions of the tympanic membrane. Synonym: plica mallearis, plica membranae tympani, Troltsch's fold. (05 Mar 2000) |
| mammary fold | Bandlike thickening of ectoderm in the embryo extending on either side from just below the axilla to the inguinal region; in human embryos, the mammary glands arise from primordia in the thoracic part of the ridge, the balance of the ridge disappearing; in some lower mammals which give birth to a litter of young, several milk glands develop along these lines. Synonym: mammary fold, milk line, milk ridge. (05 Mar 2000) |